What Are Gravitational Waves?

Polina Lukiyanova

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In the past few month, two words became the main focus point in the science world: gravitational waves. Everyone seems to be talking about them, every article mentions them, but for many people who do not take interest in the science field these aspects may appear just confusing.

Three main questions come to life when it comes to these ‘gravitational waves’: what are they? How did we discover them? And most importantly, why should we care?

Everything started back in 1905, when Einstein presented his theory of general relativity (one of the most validated theories in physics still to date), where one of the main points was the fact that space and time are linked together to create the fabric of the Universe, the so called “space-time”. His theory included various aspects such as time dilatation and all they have been proven and verified; but in 1916 he also made one last prediction: that it is possible to create ripples in the space-time fabric from an event generated by a very powerful cause, such as neutron stars or black holes orbiting around each other. These ripples are more known as “gravitational waves”; which were never detected, until now.

Going back to a billion years ago in a galaxy far away, two black holes started inspiriling one around the other, accelerating with time until they merged, releasing the energy of a billion trillion suns in a fraction of a second which is still spreading outwards in the form of gravitational waves. These waves are propagated at the speed of light, but they also weakens with distance, making them very hard to detect: the distortion that they would cause when arriving to our planet is as big as 1/1000 diameter of a proton. So, how is it possible for us to detect them?

The answer is LIGO (Laser Interferometer Gravitational-Wave Observatory). LIGO is the world’s largest gravitational wave observatory, situated in two different locations in the USA, and it currently consists of two very precise interferometers that act like ‘antennae’ to detect waves. On September 14th 2015, the structure was finally able to get data from the outer space and register the distortion caused by gravitational waves; and on the 11th of February of this year, an official document written by over a thousand authors was released, stating the following:

“On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. […] It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. […] This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.”

But what does this actually mean in terms of discovery? First we could only see light (ultraviolet, infra-red, micro-waves and radio-waves and so on), but now we get a new crystal clear view of the gravitational-wave Universe, since gravitational waves are not electromagnetic radiation and they don’t interact with matter. They carry information about their origins free of any distortion, meaning we get a whole new complementary window of the Universe that can allow us to study and analyse phenomena happening galaxies away, and maybe, the birth of the Universe itself.

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